1. Field of the Invention
The present invention relates to a method of determining a set temperature trajectory for a heat treatment system for conducting a heat-treating process, such as a film deposition process, to an object to be processed. More particularly, the present invention relates to a method of determining a set temperature trajectory for a heat treatment system to enable the heat treatment system to form a film accurately.
2. Description of the Related Art
A heat treatment step for heat-treating a wafer to form a specific film thereon is one of essential processes for fabricating a semiconductor device or the like. The heat treatment step is carried out by a heat treatment system in a high-temperature environment of a comparatively high temperature in the range of about 750 to 900xc2x0 C. Chemical vapor deposition processes (CVD processes) and oxidation/diffusion processes are such heat treatment processes.
Generally, the heat treatment system is provided with a wafer holding device (called a wafer boat) for holding a plurality of wafers in a vertically layered (tier-like) arrangement, a tubular reaction tube for containing the wafer holding device therein, a plurality of heaters formed so as to surround the side wall of the reaction tube and arranged at axial intervals, a gas supply line for carrying reactant gases to the reaction tube, and an exhaust line through which gases are discharged from the reaction tube.
Power is supplied at a predetermined rate to the heaters to maintain the wafers at a temperature suitable for film formation. It is practically impossible to measure the temperatures of the wafers during a film forming process. Therefore, usually, the measured temperature of a part other than the wafers is used for controlling the process temperature.
The control of the respective outputs of the heaters is essential to accurately achieving a heat treatment process, such as a process for depositing a film on wafers. A film deposition process will be described as an example of such a heat treatment process.
The thickness and quality of a film deposited on a wafer deviate from set values when the temperature of the wafer differs even slightly from a set wafer temperature. For example, in a certain film deposition process, a temperature difference of 1xc2x0 C. of the temperature of a wafer from a set wafer temperature causes a thickness difference of 0.1 nm of the thickness of a film from a set thickness. If the thickness of a film is in the range of several nanometers to several tens nanometers, the temperature of the wafer must be controlled in an accuracy of several degrees centigrade when the set temperature of the wafer is several hundreds degrees centigrade.
The distribution of the concentration of the reactant gas in the reaction tube is not uniform when the reactant gas flows in a constant flow from the gas supply side toward the gas discharge side of the reaction tube. If the temperatures of different zones in the reaction tube are controlled in the same way while the distribution of the concentration of the reactant gas in the reaction tube is not uniform, films respectively having different thicknesses are deposited on different wafers, respectively. Therefore, different set temperatures are set for the plurality of heaters arranged in the direction of arrangement of the plurality of wafers, respectively, and the respective temperatures of the plurality of heaters are controlled individually.
Optimum set temperatures must be determined for zones in the reaction tube respectively corresponding to the plurality of heaters through the repetition of correction of forming a film of a thickness in an allowable thickness range, in order to deposit films having accurate and uniform thicknesses on the wafers in the reaction tube.
An optimum set temperature can be determined by, for example, a method including the steps of placing a plurality of test wafers in the reaction tube, depositing films on the wafers at a set temperature, measuring the thicknesses of the deposited films by means of a measurement instrument, adjusting a set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters on the basis of the differences of the measured thicknesses from a desired thickness, and depositing films on test wafers under the adjusted set temperature condition. These steps are repeated until the differences of the measured thicknesses of the films from the desired thickness are reduced below a predetermined level. The set temperature condition thus determined is used as a set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters.
In some cases, films of different types are deposited in layers by film deposition processes when fabricating a semiconductor device. In such a case, optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters is determined for each of the film deposition processes.
Suppose, for example, that a first film is deposited on a wafer and then a second film is deposited on the first film. An optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters is determined by the aforesaid method for a first film deposition process for forming the first film. Then, an optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters for a second film deposition process for forming the second film is determined by the aforesaid method using the wafers on which the first films are deposited under the optimum temperature condition as determined above. Thus, the optimum set temperature conditions are determined individually for the films to be deposited on the wafers.
However, in some cases, the semiconductor device fabricating process needs to continuously form the first film and the second film. When forming the first film and the second film continuously, the first film is deposited on wafers loaded to a heat treatment system, and then the second film is deposited on the first film without unloading the wafers from the heat treatment system after the first film has been deposited.
When the first film and the second film are thus formed continuously, only data on the result of film deposition on the wafer on which both the first and the second film are formed can be measured by a measuring instrument, and hence the foregoing method that determines optimum set temperature conditions individually for the first and the second film cannot be used.
There are two different cases of measuring data on the result of the deposition of the first and the second film. In a first case, such as a case where both the first and the second film are nitride films, the respective thicknesses of the first film and the second film cannot be individually measured and only the sum of the respective thicknesses of the first and the second film can be measured. In a second case, such as a case where the first film is an oxide film and the second film is a nitride film, the respective thicknesses of the first and the second film can be individually measured.
In the first case, an optimum set temperature condition can be determined for the film deposition process for depositing either the first or the second film. In this case, the sum of the respective thicknesses of the first and the second film can be managed, but the respective thicknesses of the first and the second film cannot be individually managed. In addition, optimum set temperature conditions may be determined for the film deposition processes respectively for depositing the first and the second film by properly dividing data on the result of film deposition. However, practically, it is unknown whether the division (assignment) is proper. Consequently, such a film thickness management is unable to achieve the film thickness management for the individual films.
In the second case, the optimum set temperature conditions for the film forming processes for forming the first and the second film must be determined in proper order. For example, if an optimum set temperature for the film deposition process for depositing the second film is determined after forming the first and the second film, and then an optimum set temperature condition for the film deposition process for depositing the first film is determined, it is possible that the determination of the optimum set temperature condition for the film deposition process for depositing the first film affect the optimum set temperature condition for the process for depositing the second film. Thus, the optimum set temperature condition for the film deposition process for depositing the second film must be readjusted. In this case, efficient determination of the optimum set temperature conditions is difficult.
Although the film deposition process has been described as an example of the heat treatment process, the foregoing problems reside generally in heat treatment processes which are carried out by heat treatment systems.
The present invention has been made in view of such problems and it is therefore an object of the present invention to provide a method of determining a set temperature condition for a heat treatment system for carrying out a heat treatment process, such as a film deposition process for depositing a film on an object to be processed, capable of determining optimum set temperature conditions respectively for a plurality of heat treatment processes to be continuously carried out in a reaction tube.
The invention is a method of determining set temperature trajectories for a heat treatment system that continuously conducts a first heat treatment process and a second heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the first heat treatment process and the second heat treatment process conducted to the second test object to be processed; and determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the first heat treatment process and the second heat treatment process.
According to the above feature, the temporary second set temperature trajectory is corrected on the basis of the measured result of the first heat treatment process and the second heat treatment process. The first set temperature trajectory for the first heat treatment process has already been corrected before this time point and, consequently, the second set temperature trajectory for the second heat treatment process is optimized.
Preferably, the first set temperature trajectory is fixed, and the second set temperature trajectory is fixed.
In this case, difference between the objects processed simultaneously by the heat treatment system in the result of the heat treatment process, such as difference in the thickness of the films, can be reduced. The mean thickness of films formed on objects to be processed is dependent on the process temperature.
Alternatively, the first set temperature trajectory is variable, and the second set temperature trajectory is variable.
In the case, difference between parts of each object in the result of the heat treatment process, such as the thickness of the film, can be reduced in addition to the reduction of difference between the objects processed simultaneously by the heat treatment system in the result of the heat treatment process, such as difference in the thickness of the films. A proper temperature gradient can be created between a peripheral part and a central part of an object to be processed by changing the set temperature during the heat treatment process by utilizing the rate of thermal conduction in the object. Thus, the difference in the film deposition condition, such as the concentration of the source gas, between the peripheral part and the central part of the object to be processed can be offset.
In addition, preferably, the heat treatment system is divided into a plurality of zones capable of being individually heated; first set temperature trajectories are determined for the zones of the heat treatment system, respectively; the first set temperature trajectories for the zones are different from each other; second set temperature trajectories are determined for the zones of the heat treatment system, respectively; and the second set temperature trajectories for the zones are different from each other.
Thus, the method is able to effectively deal with a case where different heat treatment conditions need to be set in the direction of arrangement of the tier-like objects to be processed.
In addition, preferably, the first heat treatment process is a gate-oxide-film forming process by using thermal oxidation, and the second heat treatment process is a nitriding process for nitriding the gate-oxide-film.
Alternatively, the invention is a method of determining set temperature trajectories for a heat treatment system that continuously conducts a first heat treatment process, a second heat treatment process and a third heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the first heat treatment process and the second heat treatment process conducted to the second test object to be processed; determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the first heat treatment process and the second heat treatment process; conducting the third heat treatment process to a third test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory and to which the second heat treatment process has been conducted by using the determined second set temperature trajectory, by using a temporary third set temperature trajectory; measuring a result of the first heat treatment process, the second heat treatment process and the third heat treatment process conducted to the third test object to be processed; and determining a third set temperature trajectory for the third heat treatment process by correcting the temporary third set temperature trajectory on the basis of the measured result of the first heat treatment process, the second heat treatment process and the third heat treatment process.
In the case, based on the result of the first heat treatment process, set temperature condition in a reaction tube for the first heat treatment process can be optimized, and based on the result of the first and the second heat treatment process by using the set temperature condition, set temperature condition in the reaction tube for the second heat treatment process can be optimized. And then, based on the result of the first, the second and the third heat treatment process by using the set temperature condition, set temperature condition in the reaction tube for the third heat treatment process can be optimized. Thus, the set temperature conditions for the first, the second and the third heat treatment processes can be managed. Set temperature conditions for four or more heat treatment processes can be optimized in a similar fashion.
Preferably, the first set temperature trajectory is fixed, the second set temperature trajectory is fixed, and the third set temperature trajectory is fixed.
Alternatively, the first set temperature trajectory is variable, the second set temperature trajectory is variable, and the third set temperature trajectory is variable.
In addition, preferably, the heat treatment system is divided into a plurality of zones capable of being individually heated; first set temperature trajectories are determined for the zones of the heat treatment system, respectively; the first set temperature trajectories for the zones are different from each other; second set temperature trajectories are determined for the zones of the heat treatment system, respectively; the second set temperature trajectories for the zones are different from each other; third set temperature trajectories are determined for the zones of the heat treatment system, respectively; and the third set temperature trajectories for the zones are different from each other.
In addition, the invention is a method of determining set temperature trajectories for a heat treatment system that continuously conducts a first heat treatment process and a second heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the second heat treatment process conducted to the second test object to be processed; and determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the second heat treatment process.
In this case, set temperatures in a reaction tube concerning the result of each of the continuous heat treatment processes can be optimized. In this case, an optimum set temperature is determined for the first heat treatment process, i.e., the preceding heat treatment process, and then an optimum set temperature is determined for the second heat treatment process, i.e., the succeeding heat treatment process. Thus, readjustments of the optimum set temperature for the first heat treatment process is unnecessary, and hence the optimum set temperatures for the interior of the reaction tube can be efficiently determined.
In addition, the invention is a method of continuously conducting a first heat treatment process and a second heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the first heat treatment process and the second heat treatment process conducted to the second test object to be processed; determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the first heat treatment process and the second heat treatment process; conducting the first heat treatment process to the object to be processed, by using the determined first set temperature trajectory; and conducting the second heat treatment process to the object to be processed to which the first heat treatment process has been conducted, by using the determined second set temperature trajectory.
Alternatively, the invention is a method of continuously conducting a first heat treatment process, a second heat treatment process and a third heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the first heat treatment process and the second heat treatment process conducted to the second test object to be processed; determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the first heat treatment process and the second heat treatment process; conducting the third heat treatment process to a third test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory and to which the second heat treatment process has been conducted by using the determined second set temperature trajectory, by using a temporary third set temperature trajectory; measuring a result of the first heat treatment process, the second heat treatment process and the third heat treatment process conducted to the third test object to be processed; determining a third set temperature trajectory for the third heat treatment process by correcting the temporary third set temperature trajectory on the basis of the measured result of the first heat treatment process, the second heat treatment process and the third heat treatment process; conducting the first heat treatment process to the object to be processed, by using the determined first set temperature trajectory; conducting the second heat treatment process to the object to be processed to which the first heat treatment process has been conducted, by using the determined second set temperature trajectory; and conducting the third heat treatment process to the object to be processed to which the first heat treatment process and the second heat treatment process have been conducted, by using the determined third set temperature trajectory.
Alternatively, the invention is a method of continuously conducting a first heat treatment process and a second heat treatment process to an object to be processed, said method comprising the steps of: conducting the first heat treatment process to a first test object to be processed, by using a temporary first set temperature trajectory; measuring a result of the first heat treatment process conducted to the first test object to be processed; determining a first set temperature trajectory for the first heat treatment process by correcting the temporary first set temperature trajectory on the basis of the measured result of the first heat treatment process; conducting the second heat treatment process to a second test object to be processed to which the first heat treatment process has been conducted by using the determined first set temperature trajectory, by using a temporary second set temperature trajectory; measuring a result of the second heat treatment process conducted to the second test object to be processed; determining a second set temperature trajectory for the second heat treatment process by correcting the temporary second set temperature trajectory on the basis of the measured result of the second heat treatment process; conducting the first heat treatment process to the object to be processed, by using the determined first set temperature trajectory; and conducting the second heat treatment process to the object to be processed to which the first heat treatment process has been conducted, by using the determined second set temperature trajectory.